A phosphor to be used for e.g. a cathode ray tube, a fluorescent lamp or PDP has conventionally been produced in such a manner that raw material powders are mixed and then packed in a baking container such as a crucible and heated at a high temperature for a long period of time to carry out pyrolysis by a solid state reaction to produce a phosphor, followed by grinding by e.g. a ball mill.
However, the phosphor produced by this process comprises a powder of aggregated particles having irregular shapes. If this phosphor is applied to the above use and a fluorescent layer is formed, only an inhomogeneous fluorescent layer having a low packing density tends to be obtained, and no excellent emission properties can be obtained. Further, physical and chemical impact is applied to the phosphor in a process of grinding by e.g. a ball mill after the solid state reaction, and thus defects are likely to occur in the inside or on the surface of the phosphor particles, thus decreasing the emission properties. Further, since heating at a high temperature is conducted for a long period of time in a baking container such as a crucible, impurities from the crucible tend to be included, thus decreasing emission properties, and further, the solid state reaction may not proceed adequately depending upon the particle diameter of the raw material powders, and an impurity phase coexists, whereby no high emission properties tend to be obtained. Further, since heating has to be carried out at a high temperature for a long period of time, the energy consumed tends to be large, thus increasing the production cost of the phosphor.
In order to overcome these problems, a process has been proposed wherein a solution containing metal elements constituting a phosphor is sprayed into a carrier gas by using e.g. an ultrasonic nebulizer to obtain fine droplets, which are dried to obtain metal salt particles or metal complex particles, and these metal salt particles or metal complex particles are introduced into a pyrolysis furnace by means of a carrier gas and heated to carry out pyrolysis to obtain a phosphor. However, with this process, no adequate residue time in the pyrolysis furnace can be taken, whereby the phosphor has a low crystallinity, and activator ions can not uniformly be contained in the crystals, and further, the phosphor obtained by this process has a large number of crystal defects in the inside or on the surface of the crystals, whereby a phosphor having good emission properties can not be obtained, such being problematic.
Accordingly, in order to overcome this problem, a two-stage heating process has been proposed wherein metal salt particles or metal complex particles are subjected to pyrolysis at a relatively low temperature for short period of time to obtain a powder comprising a desired crystal phase, which is once collected, and this powder is subjected to annealing at a relatively high temperature for a long time to obtain a phosphor. With this process, the crystallinity of the phosphor particles can further be increased, and at the same time, activator ions can be contained in the crystals more uniformly, whereby a spherical phosphor having good emission properties can be obtained. However, if such an once collected powder is subjected to annealing, although crystallinity of the phosphor may be good, an extremely large number of aggregated particles tend to be formed, and accordingly a new problem has risen that a fluorescent layer will not be dense when it is formed, and no desired emission properties can be obtained.
Accordingly, the present invention has been made to overcome the above problems, and to provide a phosphor and its production process for producing a fine phosphor suitable for formation of a homogenous and dense high-brightness fluorescent film or layer when applied to e.g. a cathode ray tube, a fluorescent lamp, a PDP, a solid state lighting element, a solid state lighting apparatus, a fluorescent lamp, a vacuum fluorescent display, a luminous paint, an X-ray intensifying screen or the like, which has a narrow particle diameter distribution, which has a small amount of aggregated particles, which is spherical, which has a high purity and a uniform chemical composition, and which has excellent emission properties.